The objective of the Mars Crop Yield Forecasting Systems is to provide precise, scientific, traceable independent and timely forecasts for the main crops yields at EU level. The forecasts and analysis are used since 2001 as a benchmark by analysts from DG ¿ Agriculture and Rural Development in charge of food balance estimates. Core of the Crop Yield Forecasting System is a spatialized crop growth models that works on simulation units with assumed homogenous growth conditions. These results are aggregated at regional level to be used as yield predictors. Within this process the usage of crop masks for an accurate aggregation is envisaged. Therefore specific crop masks needs have been identified and crop masks tested.